1. Field of the Invention
The present invention is related to a disc drive, and more particularly, to a hologram disc reading and writing apparatus and a hologram disc reading apparatus.
2. Description of Related Art
With the recent progress of storage technology, discs have the advantages of large storage capacity, easy and secure storage of data, long storage term, low costs, and so on, and a user is capable of easily using a disc drive to read the data stored in the disc. Generally, the reading and writing method of a disc is to focus a laser beam on the disc through an objective lens to perform the reading and writing operation, and the storage capacity of the disc is decided by the area of the disc. To further enhance the storage capacity of the discs without changing the area of the discs, the recording density of the discs must be increased, or the wavelength of the laser beam must be shortened. However, owing to physical restrictions including diffraction limit, researchers aiming at increasing the storage capacity of the discs are facing a technological bottleneck.
For resolving the above problem, a hologram disc and a near-field disc to which the hologram technology and the near-field optic technology are applied are provided to significantly increase the storage capacity thereof. Since the storage capacity of the hologram discs can be more than 1 tera bytes (TB), and the reading speed can be more than 100 mega bytes (MB) per second, the combined mechanism of the hologram discs and a hologram disc reading and writing apparatus becomes the most promising storage medium.
FIGS. 1A and 1B are schematic diagrams of a conventional hologram disc reading and writing apparatus when writing data and reading data respectively. Referring to FIGS. 1A and 1B, a conventional hologram disc reading and writing apparatus 100 is adapted for recording data on a hologram disc 50. The hologram disc reading and writing apparatus 100 includes a signal light source 110, a liquid crystal panel 120, a reference/reading light source 130, a focusing lens 140, and a charge coupled device (CCD) 150. In a process of writing data, the signal light source 110 and the reference/reading light source 130 of the hologram disc reading and writing apparatus 100 respectively emit a signal light beam 112 and a spherical wave light beam 132 coherent with the signal light beam 112 to a data region 52 of the hologram disc 50, and the signal light beam 112 and the spherical wave light beam 132 are interfered mutually in the data region 52, such that the data are recorded in the data region 52 in the form of interference gratings. In a process of reading data, the reference/reading light source 130 emits the spherical wave light beam 132 to the data region 52 of the hologram disc 50, wherein the spherical wave light beam 132 is transformed into a data light beam 134 carrying the data after passing through the data region 52 of the hologram disc 50. The data light beam 134 is focused on the CCD 150 after passing through the focusing lens 140, and the CCD 150 transforms the data light beam 134 into an electric signal.
When the hologram disc reading and writing apparatus 100 writes data, the signal light beam 112 and the spherical wave light beam 132 together form another set of interference gratings on another data region 52′ while the hologram disc 50 rotates along a rotating direction A so as to let the data region 52′ partially overlapped with the data region 52 move to an area where the signal light beam 112 and the spherical wave light beam 132 both irradiate. Although the distribution areas of the two sets of interference gratings corresponding to the data region 52 and the data region 52′ respectively are partially overlapped, when the hologram disc reading and writing apparatus 100 reads data, the data recorded in the data region 52 (or the data region 52′) can be carried by the data light beam 134 only if the data region 52 (or the data region 52′) is completely located inside the area where the signal light beam 112 and the spherical wave light beam 132 both irradiate. In other words, in the hologram disc 50, data regions respectively recording different data can be partially overlapped, and thus the hologram disc reading and writing apparatus 100 can create large storage capacity in the restricted volume of the discs, which refers to the so-called spherical wave shifting multiplexing.
Nevertheless, the CCD 150 and the light sources (e.g. the reference/reading light source 130 and the signal light source 110) of the hologram disc reading and writing apparatus 100 are located at two opposite sides of the hologram disc 50 respectively, and this layout requires relative large space. Therefore, the volume of the hologram disc reading and writing apparatus 100 cannot be reduced, and the hologram disc reading and writing apparatus 100 is then not able to be applied in the portable electronic products with small size.